Sum of following elements in array
4 次查看(过去 30 天)
显示 更早的评论
Is there a faster way to do the following
s = rand(1, 10);
sum_following = zeros(length(s), 1);
for i = 1:length(s)-1
sum_following(i) = sum(s(i+1:end), 'all');
end
without doing
sum_following = sum(s,"all") - cumsum(s);
?
9 个评论
Walter Roberson
2023-12-9
The point is that doing this is fast but not numerically stable if the last entries of s are close to zero.
The loop with
sum(s(i+1:end), 'all');
is not numerically stable either. The trailing suffix [... A B -B -A] is going to come out as -A if abs(A) < eps(B)
Side note: You are using linear indexing. Linear indexing of anything always gives a vector result, and for a vector being added together, 'all' as a parameter does not provide any value.
Linear indexing of row vector: gives a row vector
Linear indexing of column ector: gives a column vector
Linear indexing of non-vectors: gives a result that is the same shape as the indices. Which, for i+1:end would be a row vector.
更多回答(0 个)
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Matrix Indexing 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!